Synthesis of magnetite-chitosan-starch spheres for the adsorption of red alizarin S (ARS) and Orange-II

CUEVAS RICARDO JOSÉ; FERREIRA MARÍA LUJAN

Buenos Aires

Congreso; WCCE11-11th World Congress of Chemical Engineering; 2023

Asociación Argentina de Ingenieros Químicos

The objective of this research was the synthesis of biodegradable, economical, reusable and not harmful to the environment multicatalytic solids that will be applied in adsorption for wastewater treatment. In this work these solids were characterized by adsorption of Alizarin Red S (ARS) and Orange-II (O-II) dyes. The materials were commercial chitosan of high molecular weight, glacial acetic acid 100% pure, NaOH, sodium tripolyphosphate (STPP), ferrous sulphate heptahydrate (FeSO4.7.H2O), ferric chloride hexahydrate (FeCl3.6 H2O), starch, ARS, O-II and buffer pH 11.The production of chitosan-starch-magnetite spheres with a content of magnetite between 10% and 30% and starch between 0%- 30 % was performed by a modification of a chemical co-precipitation method reported in the literature [1]. Chitosan was dissolved and later starch was added in an aqueous solution of acetic acid 5 % v/v prepared previously with the resulting iron salts solution and then mixed with magnetic stirring during 30 minutes. In parallel an exothermic alkaline aqueous solution was prepared dissolving hydroxide sodium in distillated water. Later the synthesis of spheres was performed in a glass jar with a lid that contains the alkaline solution using a plastic syringe with a needle of adequate diameter to drip the chitosan-starch containing solution and a connection of N2 that helped to mix the solution and create an inert atmosphere during the process. After washing the spheres with distillated water, a crosslinking step was carried out with an alkaline solution of NaOH and STPP during 1 h. Finally the adsorption tests were performed with a dye concentration of 20 mg/L, the temperature was 30°C and the process lasted 30 minutes. The synthesized spheres were more efficient for ARS adsorption than O-II. A possible explanation is that NH2/ -OH groups of chitosan and starch and inorganic magnetite surface interacted more efficiently with the molecules of the anthraquinonic dye than the azoic one. The best result of ARS adsorption was found with spheres containing 28% magnetite - 72% chitosan (but they fragmented during the reaction), and the worst performance corresponded to a sphere composition of 16.4% magnetite – 10.9% starch – 72.7% chitosan. Meanwhile for the azoic dye the best performance was found with spheres containing 6.7% magnetite- 20% starch-73.3% chitosan content and the worst with the 20% magnetite-17.1% starch- 62.9% chitosan composition. The magnetite present in spheres enhanced the adsorption for both dyes. It is very important to highlight that the flow rate of N2 must be small as possible during the co-precipitation process to avoid the rupture/fragilization of spheres and consequently low spheres stability for the dye adsorption. Fragmentation has to be minimized to allow reuse. A high degree of rupture could generate a higher remotion of dyes due to higher available surface.